notfred, your points are well taken and yes this seems a bit far fetched. But I think people thought that about putting somone on the moon way back when. Maybe it is a bit out there but with one of the top scientists in the world on it, I think maybe someday it could be viable. Of course, you are an engineer and I'm just a writer, so I could be wrong! This is why it's great when our readers weigh in on stories to provide real-world perspective.

I don't understand why people keep thinking this is a viable thing. In order to be useable you'd need to construct a system capable of delivering 500GW to 1000GW of electricity on Earth, comparable to a standard power station, otherwise, what's the point. First off the space based panels would have to be made of galium arsenide to withstand the radiation in space. Ordinary silicon panels would die after 6 months to a year. Galium Arsenide panels are 50X more expensive, even if they are 40% efficient. At an overall system efficiency of about 7% (panel efficiency = 40%, convert to microwave = 75%, atmospheric losses 50%, receiving antenna losses = 75%, convert to 60 Hz AC = 60%) .4 x .75 x .5 x .75 x .6 = .67) we'd need a huge solar array. At 100% efficiency we'd need the total panel size to be 1000GW/1400watt per foot = 714,000 sq ft. At 7% overall efficiency the panel size would be over 10 million sq feet. That's 2/3 of a mile on a side. And what keeps the panels all in the same plane? A giant truss of some kind. Currently the solar panels on the ISS are the largest we have in space. Do any readers recall the frequent problems they've had? These are microscopic compared to our sci-fi panels! And how will you keep something this large pointed at the sun? It becomes a giant solar sail.. constantly being pushed away by the sun. It would have to be in geo-synchronous orbit and sending it's 1000GW microwave beam through the path of thousands of satelites in lower orbit. And how do you maintain it? What about space debris.. this thing will make a nice target! And how do you even get it up there in the first place? We'd be talking about 1000's of launches!! And you want robots to assemble it? What robots? This thing would probably cost more than the GNP of the entire world!! I could go on and on. This whole idea is ridiculous!

Next thing we know, someone will propose putting solar panels on roads! Yes, I know, they already have, and if you believe that will work, I guess you might as well believe this too.

Sorry for being so sarcastic and perhaps exagerating a tad.. but I just get tired of these crazy schemes! I run an engineering company and it seems half of my time is spent explaining to clients why some things are just not practical!!

Credentials: I have been working space solar arrays for over 35 years. My college project was Space Solar Power Systems (SSPS) later called SBSP originally suggested by 1941 Asimov SF and later made credible by Peter Glaser in a US patent for "practical" application. (See Wiki for more in depth). SiliconGreybeard is right, low power microwave beamed to earth surface receiver/converters (rectenna size:square miles) was the generally agreed upon technique for safe delivery and conversion. Jaffe of NRL is correct in a key need was a distributed beaming capability which will subsequently need to be synchronized to avoid nulling of the beamed power at the receiver. I have designed and built solar arrays (S/A) which have lasted on orbit for over thirty years with graceful (predictable) degradation in Geosynch orbit where these should be parked. That's not an issue. But fm and Daniyal_Ali are also right. Here is the challenge: at 0.10/ kWhr, and 30 years of perfect operation, it leaves only $26.2/watt to build and deliver the complete system (not including amortized nonrecurring costs). The industry shows space rated arrays typically cost between $600 to $5000/watt. Current terrestrial solar panel technology which might be capable for space use may get to $4/watt, though the terrestrial ones are looking to eventually <$1/watt wholesale, but space is tough! To go from $600/W to $4/watt for space S/A is beyond current technology. Next, the cheapest cost to space at Geo is ~10000/lb, though SpaceX hopes to get that in the realm of $1000/lb. Space S/A weigh 14 to 36 W/lb, though there is some hope to get to 180 W/lb eventually. That is $.05lb/watt or $50/watt for launch. Launch cost would need to get below $200/lb ($10/W) to make the system feasible. Then you need to pay for the ground based rectennas and all the balance of system with the $26-$4-$10=$12/W left over. Possible? Yes. Near term (next 30 years)? No. Should we do it? Ultimately for the species, yes. More cost effective than terrestrial solar? In 50 years? That's TBD.

Thank you for that thorough evaluation of this system, fm. According to your calculations it seems that the economics don't add up, but I suppose that's up to the Navy to find out and decide, and perhaps they have a workable solution to solve this problem.

Interesting discussion! Just to put some perspective on this - the power we receive from the sun on a bright sunny day is on the order of 1000 Watts per square meter. Divide by 5, = 200 W/m2, and that's what you can collect from a PV panel. In Iowa, we can count on about 4 hrs of sunlight average per day, so if we had that power on round-the-clock, we'd get 6x what we can get using current technology. That's the minimum bar for one of these systems.

At $3/watt for PV, we would require a space-based system that costs less than $18/watt. A satellite that could deliver 1 MW of power to earth that costs $18M? With transmission losses, optimistically we're talking a satellite(s) that has 4MW of PV panels. I see a few issues with these numbers:

Space-capable PV would have to cost < $4/watt. I haven't priced this stuff, but i'm sure it's much more than that now.

Space-capable PV needs to be replaced every 6 years or so, with a max lifetime of 20 years, and is highly susceptible to meteorite damage.

Avoiding space debris is a full-time job for any orbital platform, and avoiding the junk means moving the platform (have you seen the movie "Gravity"?). Moving the platform means maintaining proper aim of the "power beam" while it's moving.

The ISS has a 1 acre array of about 90 kW. This would have to be 40 *times* that size. 40 ACRES of PV in space - that is capable of being pushed around by rockets to avoid space junk without collapsing on itself. And while maintaining pinpoint aim during the whole maneuver.

This is just for a SINGLE 1MW space-based satellite. By inspection, this is not an $18M satellite; i can't count high enough to give an estimate on what this would really cost.

We can do this job much cheaper, much more reliably, far longer-lasting, and with currently-available hardware today here on terra firma. Space-based power is gee-whiz, but the reality just isn't there.

Death rays. Yes the Navy is working on microwave and laser death rays.

"The interest of U.S. Navy in exploring the use of High Power Microwave (HPM) techniques and technologies for purposes of building anti-ship missile defense (ASMD) and command and control warfare (C2W) would likely encourage joint proposals wherein the project would be executed in a Naval Research Laboratory (NRL)/contractor team format to get the maximum amount of research in the most efficient manner."

http://ubiquity.acm.org/article.cfm?id=1226693

The design of the solar panel modular system will have to have active steering, and the best way to do that is with phased array tech. That same phased array steering can be used to concentrate the beam and steer it any place you want.

Maybe the Navy will just use it to knock out enemy electronics, but the 1 GW version will cook a person or tank before they can react.

I think I am a bit confused by all this talk of "death beams." I know these type of waves could potentially be dangerous (as is sunlight if we are overexposed to it), but do people really think the Navy is doing something that is harmful to humans?

I think this is the general idea, jhankwitz. The robots would be controlled by humans but save humans from actually having to go into space to deploy the satellites. I think in the long run it would be more efficient and cost effective, even if there is a lot spent in initial R&D and cost.

A few weeks ago, Ford Motor Co. quietly announced that it was rolling out a new wrinkle to the powerful safety feature called stability control, adding even more lifesaving potential to a technology that has already been very successful.

It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.

People who want to take advantage of solar energy in their homes no longer need to install a bolt-on solar-panel system atop their houses -- they can integrate solar-energy-harvesting shingles directing into an existing or new roof instead.

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